This research has two major objectives. The first is to elucidate the mechanism of initiation of DNA replication. A specialized transducing bacteriophage carrying the chromosomal origin of replication and lacking a phage origin of replication has been constructed and is being used to study regulation of initiation in temperature sensitive dna host mutants. New mutants with defects in the initiation gene dnaA are being isolated and used to study the role of this gene in the initiation process. The second objective of this work is to study the mechanism of secretion of periplasmic and outer membrane proteins in E. coli. In particular we wish to know which regions of polypeptide structure determine the final location of these proteins.